Antiviral interferons provide critical host defense mechanisms against viral infection. In the absence of IFN signaling, the host may be susceptible to lethal viral infection. IFNs protect host cells from viral disease by transcriptionally inducing hundreds of interferon-stimulated genes, which encode a variety of direct antiviral effectors and modulators of host defense signaling pathways. Our recent screening efforts have sought to identify novel human antiviral ISGs, characterize their mechanisms of action, and determine their specificity across a broad range of highly diverse viruses. The viruses of interest include several pathogens that are emerging or re-emerging infectious disease threats. Many of these viruses are transmitted to humans from natural animal reservoirs. Among the numerous reservoir hosts, bats are particularly unique in their ability to harbor highly pathogenic viruses with little to no overt disease. The mechanistic basis for the resistance of bats to viral disease s currently unknown, but several lines of evidence point to a potentially unique innate immune system. The goals of this project are to institute a bat ISG discovery pipeline, with an emphasis on the identification and characterization of novel antiviral mechanisms. Experimentally, we will synthesize a targeted bat ISG library using available bat genomic data. In parallel, we will establish methods for antiviral ISG enrichment from IFN-treated bat cells. Our previous cell-based flow cytometry screening platform will be miniaturized for rapid testing of bat ISGs against numerous viruses in a variety of bat and human cell lines. Follow-up mechanistic studies include the use of molecular virological tools to determine ISG modes of action in the viral life cycle, in addition to biochemical, genetic, and cell biological approaches to uncover th host-based mechanisms of antiviral action.